"We're running for mayor and we intend to win," he said at a Houston fundraiser captured by journalist Jose de Jesus Ortiz.
Whitmire, a Democrat, was joined by several other Houston lawmakers at the event, including his Senate colleague Borris Miles. He told the Houston Chronicle that he intends to run for reelection to the Senate in 2022, serve in the 2023 legislative session and then run for mayor in November that year.
He told the newspaper a public announcement will come later but "it's no secret" that he plans to run for mayor.
Whitmire was not available for comment Thursday afternoon.
Whitmire has served in the Senate since 1983. Prior to that, he served 10 years in the Texas House of Representatives.
The announcement confirmed a move that was rumored for months and made Whitmire the first candidate to publicly announce his intention to succeed Sylvester Turner as the mayor of the state's most populous city. Houston has term limits, and Turner's second and final term will end in January 2024.
Lt. Gov. Dan Patrick often alluded to Whitmire's possible run during this year's special legislative sessions. The lieutenant governor would usually ask Whitmire, who holds the honorary title of "dean of the Senate" as its longest-serving member, to adjourn the chamber's proceedings. But during the third special session, Patrick would often call instead on state Sen. Judith Zaffirini, D-Laredo, the body's second-longest serving member, and refer to her as the "dean-in-waiting."
In the Senate, Whitmire is best known for his work on criminal justice and public safety. A longtime Houston politician, Whitmire holds close ties to the city's public employee unions, including the police and fire unions.
Whitmire has $11 million in his political war chest, a considerable head start for a candidate running a mayoral election.
The Texas Tribune is a nonpartisan, nonprofit media organization that informs Texans — and engages with them – about public policy, politics, government, and statewide issues.